In prior work two dimensional proton NMR methods were used to confirm, correct, or assign de novo the proton resonances of the heme and over half the amino acids in horse ferrocytochrome c. Also a number of residues have been assigned in other cytochromes c. A complete assignment of these related proteins would provide an unparalleled resource for studies of protein structure and dynamics. This would also provide an exceptional system for testing and using emerging NMR techniques. Preliminary results indicate that several effects earlier thought to pose serious barriers to the application of these methods to larger proteins (e.g. spin diffusion, T1 and T2 effects) are in fact not a problem. We therefore propose to apply these assignment strategies, already proven successful, to complete the assignment of the horse enzyme. Success here will provide the key to the rapid further assignment of additional ferrocytochrome c species (five are proposed) and their oxidized counterparts. NMR techniques will be used to define local secondary structure and dynamics and the effects thereon of change in redox state and amino acid substitution. Structure will be determined from the time dependence of the NOE and coupling constants. Structural dyamics covering the range between subnanoseconds and seconds will be studied. The majority of motional information will be derived from relaxation data and chemical exchange effects in the NOESY experiment. Overall these results are expected to provide interesting insights into protein structure-function relationships as well as protein structural dynamics.